DIET AND PERFORMANCE
Kirwan, J. P., Costill, D. L., Mitchell, J. B., Houmard, J. A., Flinn, M. G., Fink, W. J., & Beltz, J. D. (1988). Carbohydrate balance in competitive runners during successive days of intense training. Journal of Applied Physiology, 65, 2601-2606.
Endurance runners who consumed a 50 percent carbohydrate diet experienced a decrease in muscle glycogen stores, a decrease in running economy, and an increased perception of fatigue following a five-day increase in training load. For a group that was placed on an 80 percent carbohydrate diet, only limited glycogen depletion was recorded. Thus, the concentration of carbohydrate in the diet will affect performance efficiency, recovery, and the psychological perceptions of training intensity.
Not only the amount but the type of carbohydrate that is ingested is important for competitive and training performances. Costill, Sherman, and Fink (1981) looked at the effects of simple carbohydrates (e.g., pancakes, syrup, candy, a glucose drink) and complex carbohydrates (e.g., potatoes, pasta, whole wheat bread) on the recovery of muscle glycogen after glycogen depletion. They found no difference within the first 24 hours of recovery. However, complex carbohydrates produced significantly more muscle glycogen synthesis within the next 24 hours. This finding is important. Not only does it support the use of complex carbohydrates over simple sugars as a dietary necessity, but it also indicates that what is consumed between stages in a prolonged staged-competition, such as the Tour de France, will directly affect recovery and energy stores. Carbohydrates can be readily replaced in fluid form as well as in appropriate foods. After each day's event it is necessary to ensure that complex carbohydrate loading is continued to maximize the restoration process. Thus, diet within prolonged competitions is an important factor for determining recovery speed and quality between exercise bouts or events.
Return to Table of Contents for this issue.